An example of a conventional brush holder assembly for use in a direct-current electric motor is disclosed in Japanese Utility Model Laid-Open No. HEI 3-18658. The construction of the conventional brush holder assembly will be explained below with reference to FIGS. 7 to 11.
The brush holder assembly comprises a pair of negative-side brush holder frames 2a, 2b and a pair of positive-side brush holder frames 3a, 3b fastened to a base 4.
The base 4 is a steel plate formed into an annulus having a central opening 4a being designed to allow passage of a commutator 1. A plurality of tabs 21 are disposed on the base 4 by press working part of the base 4.
Furthermore, the brush holder frames 2a, 2b, 3a, 3b are molded from electrically-insulating synthetic resin.
Brush receiving recesses 22 are disposed in brush holder frames 2a, 3b, respectively, so as to extend from a first end towards a second end without penetrating the second end. Furthermore, pairs of flanges 23 are disposed such that each extends outwards from a central portion of the bottom end on either side. Fastening slots 24 are disposed on each pair of flanges 23. Furthermore, a lead outlet groove 25 is disposed on one side so as to extend from the first end towards the second end and join the brush receiving recess 22 to the outside. Furthermore, a plurality of radiator openings 27 are provided.
On the other hand, brush holder frames 2b, 3a are constructed similarly to brush holder frames 2a, 3b above, except that the lead outlet groove 25 is disposed on the opposite side of each so as to extend from the first end towards the second end and join the brush receiving recess 22 to the outside.
The brush holder frames 2a, 2b, 3a, 3b are fastened onto the base 4 by passing the tabs 21 through the fastening slots 24 and bending the tips of the tabs 21 projecting from the fastening slots 24. At that point, the brush holder frames 2a, 2b, 3a, 3b are fastened to the base 4 such that the open ends of the brush receiving recesses 22 each face the central opening 4a of the base 4 and the axes of the brush receiving recesses 22 pass through the central axis of the central opening 4a of the base 4. The tabs 21 securing each of the brush holder frames are bent in mutually opposite radial directions, preventing the brush holder frames from dislodging in the axial direction.
Negative-side brushes 5a, 5b are inserted into the brush receiving recesses 22 of brush holder frames 2a, 2b, respectively, by passing negative-side leads 7a, 7b through the lead outlet grooves 25. Similarly, positive-side brushes 6a, 6b are inserted into the brush receiving recesses 22 of brush holder frames 3a, 3b, respectively, by passing positive-side leads 8a, 8b through the lead outlet grooves 25. The brushes 5a, 5b, 6a, 6b are placed in contact with the outer circumferential surface of the commutator 1 inserted through the central opening 4a of the base 4 by the force of brush springs 9 disposed within each of the brush receiving recesses 22.
The negative-side leads 7a, 7b connected to the negative-side brushes 5a, 5b and forming a pigtail are grounded by connection to the base by welding, etc. On the other hand, the positive-side leads 8a, 8b connected to the positive-side brushes 6a, 6b and forming a pigtail are connected to a power source (not shown) by means of a connector 11. The positive-side leads 8a, 8b are covered with insulating tubing 10 to prevent electrical short-circuiting with the base 4.
This brush holder assembly is mounted on an end bracket of direct-current electric motor using screw holes 12 disposed in the base 4.
In a conventional brush holder assembly, the positive-side brush holder frames 3a, 3b are secured to the base 4 by passing tabs 21 disposed on the base 4 through the fastening slots 24 disposed in the flanges 23 extending outwards from central portions of the bottom end on either side thereof and bending the tips of the tabs 21 projecting from the fastening slots 24. Thus, as shown in FIG. 11, the tabs 21 and the leads 8a, 8b are in close proximity. Moreover, as the brushes 6a, 6b are worn down by the commutator 1, they are moved towards the commutator 1 by the force of the brush springs 9. With the movement of the brushes 6a, 6b towards the commutator 1, the leads 8a, 8b move within the outlet grooves 25 towards the commutator 1.
During operation of the direct-current electric motor, the leads 8a, 8b are on the positive electrode side, and the base 4, including the tabs 21, is on the negative electrode side. Thus, it has been necessary to cover the leads 8a, 8b with the insulating tubing 10 because there is a risk that the leads 8a, 8b and the tabs 21 will touch and short circuit electrically. For that reason, a problem has been that because of the necessity to have the tubing 10, an operation for covering the leads 8a, 8b with the tubing 10 has been required, making it difficult to reduce costs.